The invention relates generally to power-driven conveyors and, more particularly, to driven roller-top conveyor belts in which the rollers are themselves driven by a drive belt beneath the roller-top belt along a carryway segment of a conveying path.
Conveyors are used in industrial applications to transport articles from one processing station to another. Often a continuously moving conveyor belt is used to deliver articles to a downstream processing station. As soon as the supply of articles exceeds the handling capacity of the downstream processing station, the articles begin to back up upstream of the processing station. Friction between the conveying surface of the moving belt and the backed-up, or accumulated, articles causes the articles to push against each other. The pressure exerted against the article at the front of the group of accumulated articles is called back line pressure. As more articles back up, the back line pressure increases. Back line pressure can cause damage to the articles, excessively load the conveyor belt and its drive components, and accelerate belt wear. Roller-top belts with freely rotatable rollers in rolling contact with the undersides of conveyed articles are often used to reduce friction and lower back line pressure. But even roller-top belts cannot decrease back line pressure to zero by themselves. Zone accumulation, in which a series of separately driven conveyors can be stopped and started depending on the downstream demand and upstream supply of articles, is used to eliminate back line pressure. But zone accumulation requires multiple drives and sensors, which can be costly, and, between consecutive conveying zones, transfers, at which articles are susceptible to tipping.
Consequently, what is needed is a true zero back pressure conveyor that does not have the article-tipping potential of zone accumulators.